The technology of the present disclosure relates to catalyst particles, a catalyst ink, an electrode catalyst layer for a fuel cell, a membrane electrode assembly, and a polymer electrolyte fuel cell. The present disclosure further relates to a manufacturing method thereof. More specifically, the present disclosure relates to a method of manufacturing a catalyst ink and an electrode catalyst layer using catalyst particles comprising carbon particles supporting a catalyst material.
A polymer electrolyte fuel cell having a polymer electrolyte membrane as ion conductor is known as one type of fuel cells to directly convert the reaction energy of a raw material gas to electrical energy. The polymer electrolyte fuel cell is promising as an energy source of automobiles, railways, cogeneration systems, and the like because of its shorter startup time than that of other fuel cells and its capability of operating at normal temperature.
Although such a polymer electrolyte fuel cell is excellent in terms of startup time and operating temperature as described above, the problem for further implementation is that the power generation efficiency is low. Accordingly, various proposals for increasing the output voltage have been conventionally made in manufacturing technology of a polymer electrolyte fuel cell. For example, in the technique disclosed in Japanese Laid-Open Patent Publication No. 2010-257929, the relative permittivity of solution containing an ionomer is controlled within a predetermined range during manufacturing of a catalyst ink for forming an electrode catalyst layer. This is intended to increase ionomer coverage for catalyst particles.
In other words, increase in ionomer coverage for a support carbon material as a catalyst material supporting carbon is intended. Due to the increased uniformity of the support carbon material and the ionomer in an electrode catalyst layer, the utilization efficiency of catalyst particles in a membrane electrode assembly is increased, so that the output voltage of a polymer electrolyte fuel cell is intended to be increased.
In a specific technique disclosed in the Japanese Laid-Open Patent Publication No. 2010-257929, a dispersion liquid in which catalyst particles are dispersed and a solution of ionomer having a relative permittivity of 30 or more are prepared, respectively. The dispersion liquid and the solution of ionomer are then blended with each other to form a mixture liquid. A dispersion medium having a relative permittivity of 20 or less is added to the mixture liquid. This is intended to prevent the aggregation and gelation of the ionomer, so that the viscosity of the solution rises to the viscosity required for production of an electrode catalyst layer. In other words, performing these steps is intended to increase the ionomer coverage for catalyst particles in a catalyst ink.
In the step of adding the dispersion medium having a relative permittivity of 20 or less to the mixture liquid in which the ionomer is prevented from aggregating or gelating, however, the aggregation or gelation of ionomer locally occurs to no small extent, so long as the dispersing medium is nonuniformly added to the mixture liquid. It is difficult to uniformly add the dispersion medium to the mixture liquid to an extent not causing gelation or aggregation of the ionomer in the first place. In short, in order to increase the output voltage of a polymer electrolyte fuel cell, room for improvement still remains even in the technique described above.
The object of the present disclosure is to increase the output voltage of a polymer electrolyte fuel cell.